Method of manufacturing magnetic heads



March 1, 1966 G. J. MANDERS METHOD OF MANUFACTURING MAGNETIC HEADS FiledSept. 6. 1960 BY M AGE IJ:

United States Patent 3,237,280 METHOD OF MANUFACT MAGNETHQ HEADSGodefridus Johannes Manders, Eindhoven, Netherlands, assignor to NorthAmerican Philips Company, Inc, New York, N.Y., a corporation of DelawareFiled Sept. 6, 1960, Ser. No. 54,278 Claims priority, applicationNetherlands, Sept. 5, 1959, 243,049 7 Claims. (Cl. 2155.5)

The invention relates to a method of manufacturing a magnetic headhaving two or more parallel gaps lying one after the other and tomagnetic heads manufactured by this method.

Magnetic heads having two parallel gaps lying one after the other may beemployed for many purposes. One gap may, for example, be used as arecording gap and the other as a scanning gap; thus the recording andreproducing head is combined in a single magnetic head, which may be ofadvantage in recording pulses, when the recorded signal is to be checkedimmediately.

Such a combination is also required when the head is to be used inconjunction with a magnetic record carrier moved at a very low rate (forexample 9 cms. per second) and it is a further requirement to record aconsiderable frequency band (for example up to kc./s.). With theserequirements it is not possible to use compromise values for therelatively opposite requirements with respect to the gap lengths for therecording and scanning gaps. It appears that a satisfactory recording ofthe magnetic carrier throughout the depth of the magnetic layerrequires, regardless of the speed of the magnetic carrier, an optimumgap length of about 11.. For reproduction, however, the optimum value ofthe gap length depends not only upon the desired frequency spectrum butalso, to a great extent, upon the speed of the magnetic carrier thus itmust be sufficiently smaller, for example, by a factor 2, than theshortest recorded wavelength. In a given case the length of the scanninggap may amount The directions of these gaps with respect to the magneticcarrier must, of course, be the same. Only a small tolerance (.21difference in direction of 3 with a track width of 3 mms. and a velocityof the magnetic carrier of 9.5 cms./ sec.) is admissible.

Such a high accuracy in the relative positions of the two gaps can, inpractice, he realized only when the two heads, ie, the recording and thereproducing head, are mechanically rigidly secured to each other; evenwhen they are thus secured, however, an adequately accurate relativelyparallel position of the two gaps cannot be ensured without furthermeans.

The invention provides a simple, efiicient means to attain theabove-stated desirable accuracy.

In accordance with the method of the invention, the magnetic corehalves, of which the pole shoes form pairwise the boundaries of thegaps, the relatively opposite halves of each pair of adjacent,individual magnetic circuits, together with the material providedbetween these halves are connected to form a fixed unit (inner unit)constituting a rigid mechanical assembly, after which the two headsurfaces of this unit, on which the other core halves provided withwindings are to bear, are ground to be planoparallel.

The head described above, having one recording gap and one reproducinggap, may also be employed for the reproduction of a sound withreverberation by means of the feed-back of the circuit including thereproducing gap to the circuit of the recording gap. In special cases itmay be desired, however, to provide a delay for each individualloudspeaker provided in the reproducing space ice and connected to thereproducing circuits. This may be achieved by means of a magnetic headhaving at least two reproducing gaps. In principle, use could be made tothis end of a magnetic head with two gaps, provided it is used inconjunction with a magnetic record carrier moved at a conventional rate,at least at a rate of more than 10 ems/sec. However, if the advantage ofa magnetic head having a separate recording gap and separate reproducinggaps for use in conjunction with a magnetic record carrier moved withvery low speeds is to be obtained, this head is to be provided withthree or more gaps.

In order to obtain an accurately parallel orientation of these gaps,each of the other core halves provided with the windings is connected,by the method according to the invention in the manner in which theinner unit described above is manufactured, with a core half of afurther individual circuit to obtain a mechanical unit (intermediateunit). Such a head is capable of producing echo eifects in aconventional manner when either the number of reproducing gaps is chosenhigh or when, in the case of a smaller number of reproducing gaps, acircuit of one of them is fed back to that of the recording gap. At anyrate, when using such a multigap magnetic head, it is ensured that in alarge reproducing space each of the various loudspeakers can have itsindividual delay and, more over, that the reproduced sound may have echoeffects.

According to a further aspect of the method according to the inventionfoils of the thickness of the desired gap length are clamped in at thearea of the gaps, when the other intermediate units or end core halvesare applied to the end surfaces of the inner units and intermediateunits respectively; thus two or more most accurately parallel gaps ofprecisely the desired length are obtained.

The invention will now be described more fully with reference to thedrawing.

FIG. 1 is a sectional view of the two inner core halves and theintermediate connecting and screening material.

FIG. 2 is an elevation of the left-hand sidewall of the unit shown inthe sectional view of FIG. 1.

FIG. 3 is an elevation of one of the outer core halves and the windingslipped onto it.

FIG. 4 is a sectional view of a complete reproducing head.

FIG. 5 is a sectional view of an intermediate unit according to theinvention.

FIG. 6 is a sectional view of a complete magnetic head comprising aninner unit, an intermediate unit on the left and right-hand sidesthereof, and an end core half on the extreme left-hand side and on theextreme righthand side thereof.

FIGS. 7 and 8 show a double recording and reproducing head forstereophony.

The workpiece shown in FIGS. 1 and 2 consists of the two inner corehalves 1 and 2, the shape of which is illustrated in FIG. 2 and whichare combined by an intermediate layer 3 of a plastic or similar bondingmaterial to form a fixed unit. Between the core halves 1 and 2 amagnetic screening 4 may be provided in the layer 3.

The head surfaces 18 of this workpiece formed by the parts it to 4 areground (lapped) to be accurately pl-anoparallel. Then the two other corehalves 5 and 6, of which one is shown in FIG. 3, are ground to accuratefiatness on the free sides. The windings 9, of which oniy one is shownin FIG. 4, are then slipped onto these core halves 5 and 6, after whichthe latter are urged against the two planop'ara'llel head surfaces onthe inner core halves, in which position they are secured with the aidof a cast resin 7 and 8. Between the engaging poleshoes 10 and 11 of thecore halves is arranged a foil 12 having a thick ness of the gap lengthdesired locally, for example, 30p.

with the recording gap and 3 1 with the reproducing gap; this foil isheld clamped tight between the poleshoes.

The most favorable length for the two gaps and an accurately parallelorientation of the two gaps are thus ensured in a simple manner.

The intermediate unit shown in FIG. 5 consists of a core half 14,provided with windings 13, as is shown in FIG. 3, and a core half of afurther individual magnetic circuit, between which is arranged amagnetic screening 16, as in the workpiece shown in FIG. 1, after whichthe assembly is secured with the aid of cast resin 17. The head surfaces19 of this unit are then ground to flatness, and subsequently the innerunit and the intermediate unit, with the interposition of a foil 20between the engaging poleshoes 10 and 21 of the core halves 2. and 14respectively, are secured to each other. The magnetic head shown in thecompleted state in FIG. 6 comprises an inner unit as shown in FIG. 1 andon the righthand side thereof an intermediate unit as shown in FIG. 5and on the left-hand side thereof a similar intermediate unit, while onthe extreme left-hand side and on the extreme right-hand side the endcore halves as shown in FIG. 4 are arranged. If with this head havingfour gaps a special, larger recording gap length can be provided, thisis to be provided, as a matter of course, at the place of the first gap.

The invention may also be used with a recording and reproducing head fora double sound track, for example, for stereophony. It is required inthis case that the four gaps, is. two for the upper track and two forthe lower track, should lie pairwise in accurately parallel planes.

First the four inner core halves with their screening means andfastening means are composed, the outer surfaces of this assembly areground to be accurately planoparallel and the outer core halves arepairwise arranged thereon in the manner as described above for thesingle head.

This is illustrated in FIGS. 7 and 8. The workpiece to be ground to aplanoparallel shape consists of the four inner core halves 23, 24, 25and 26, the connecting material 27 and the screening members 28 and 29.After the head surfaces 22 of this workpiece have been ground off, thefour outer core halves 30, '31, 32 and 33 are pairwise embedded infastening pieces 34 and 35 respectively, and urged against theassociated inner core halves, after having been ground to flatness;foils of the thickness of the desired gap length may be used at theplace of the poleshoes. Thus all requirements are fulfilled; therecording gaps are in line with each other and extend precisely parallelto the reproducing gaps, which are also aligned, and each gap has thelength desired.

While the invention has been described with respect to specificembodiments, various modifications thereof will be apparent to thoseskilled in the art without departing from the inventive concept, thescope of which is set forth in the appended claims.

What is claimed is:

1. A method of manufacturing a magnetic head having at least twoparallel non-colinear gaps each lying between the poleshoes of amagnetic circuit consisting of two adjacent core halves, comprising:forming a mechanically rigid assembly of two core halves belonging todifferent magnetic circuits, said assembly having exposed noncolinearpoleshoe faces, grinding said poleshoe faces until they aresubstantially plano-parallel, placing the poleshoe faces ofcorresponding core halves against the two ground poleshoe faces of theassembly, and mechanically securtin-g said corresponding core halves inposition.

2. A method of manufacturing a magnetic head having at least twoparallel non-colinear gaps each lying between the poleshoes of amagnetic circuit consisting of two adjacent core halves, comprising:forming a mechanically rigid assembly of two inner core halves belongingto different magnetic circuits, said assembly having exposednon-colinear poleshoe faces, grinding said poleshoe faces until they aresubstantially plane-parallel, placing the poleshoe faces ofcorresponding outer core halves having electrical windings coupledthereto against the two ground poleshoe faces of the assembly, andsecuring said corresponding outer core halves in position 3. A method ofmanufacturing a magnetic head having at least two parallel non-colineargaps each lying between the poleshoes of a magnetic circuit consistingof two adjacent core halves, comprising: forming a mechanically rigidassembly of two core halves belonging to different magnetic circuits,said assembly having exposed noncolinear poleshoe faces, grinding saidpoleshoe faces until they are substantially plano-parallel, placing anon-mag netic spacer against each poleshoe face, placing the poleshoefaces of corresponding core halves against the two ground poleshoe facesand non-magnetic spacers of the assembly, and mechanically securing saidcorresponding core halves in position. I

4. A method of manufacturing a magnetic head having at least twoparallel non-colinear gaps each lying between the poleshoes of amagnetic circuit consisting of two adjacent core halves, comprising:forming a mechanically rigid assembly of two inner core halves belongingto different magnetic circuits, said assembly having exposed noncolinear poleshoe faces, grinding said poleshoe faces until they aresubstantially lano-parallel, placing a nonmagnetic spacer against eachpoleshoe face, placing the poleshoe faces of corresponding outer corehalves having electrical windings coupled thereto against the two groundpoleshoe faces of the assembly, and securing said corresponding outercore halves in position.

5. A method of manufacturing a magnetic head having at least threeparallel non-colinear gaps each lying between the poleshoes of 'amagnetic circuit consisting of two adjacent core halves, comprising:forming a first mechanically rigid assembly of two core halves belongingto different magnetic circuits, said assembly having exposednon-colinear poleshoe faces, grinding said poleshoe faces until they arelano-parallel, forming second and third mechanically rigid assemblies oftwo core halves with exposed poleshoe faces belonging to differentmagnetic circuits, one of the core halves of each of said second andthird assemblies having electrical windings coupled thereto, grindingthe exposed poleshoe faces of the second and third assemblies until theyare substantially plano-parallel, placing the corresponding ground facesof the core halves of the second and third assemblies respectivelyhaving electrical windings coupled thereto against the two ground facesof the first assembly, and mechanically securing said assemblies inposition.

6. A method of manufacturing a magnetic head having at least threeparallel non-colinear gaps each lying be tween the poleshoes of amagnetic circuit consisting of two adjacent core halves, comprising:forming a first mechanically rigid assembly of two core halves belongingto different magnetic circuits, said assembly having exposednon-colinear poleshoe faces, grinding said poleshoe faces until they aresubstantially plano-parallel, forming second and third mechanicallyrigid assemblies of two core halves 'with exposed poleshoe facesbelonging to different magnetic circuits, one of the :core halves ofeach of said second and third assemblies having electrical windingscoupled thereto, grinding the exposed pedeshoe faces of the second andthird assemblies until they are substantially plano-parallel, placing anon-magnetic spacer against each poleshoe face of the first assembly,placing the corresponding ground faces of the core halves of the secondand third assemblies respectively having electrical windings coupledthereto against the two ground faces and non-magnetic spacers of thefirst assembl and mechanically securing said assemblies in position.

7. A method of manufacturing a magnetic head having at least threeparallel non-colinear gaps each lying between the poleshoes of amagnetic circuit consisting of two adjacent core halves, comprising:forming a first mechanically rigid assembly of two core halves belongingto different mlagnetic circuits, said assembly having exposednon-colinear poleshoe faces, grinding said poleshoe faces until they aresubstantially planoparal'lel, forming second and third mechanicallyrigid assemblies of two core halves with exposed pole-shoe facesbelonging to different magnetic circuits, one of the core halves of eachof said second and third assemblies having electrical Windings coupledthereto, grinding the exposed poleshoe faces of the second and thirdassemblies until they are substantially plane-parallel, placing anon-magnetic spacer against each poleshoe face of the first assembly,placing the corresponding ground poleshoe faces of the core halves ofthe second and third assemblies respectively having electrical windingscoupled thereto against the two ground faces and non-magnetic spacers ofthe first assembly, completing the magnetic circuits of the other corehalves of the second and third assemblies by placing a plurality ofother core half assemblies in contiguous relation to said second andthird assemblies, and mechanically fixing securing said assemblies inposition.

References Cited by the Examiner UNITED STATES PATENTS 2,915,812 12/1959Rettinger 29155.59 2,967,750 1/ 1961 Koren 179100.2

FOREIGN PATENTS 884,881 5/1953 France. 1,213,217 10/1959 France.

800,233 8/ 1958 Great Britain.

WHITMORE A. WILTZ, Primary Examiner.

NEWTON N. LOVEWELL, JOHN F. CAMPBELL,

Examiners.

1. A METHOD OF MANUFACTURING A MAGNETIC HEAD HAVING AT LEAST TWOPARALLEL NON-COLINEAR GAPS EACH LYING BETWEEN THE POLESHOES OF AMAGNETIC CIRCUIT CONSISTING OF TWO ADJACENT CORE HALVES, COMPRISING:FORMING A MECHANICALLY RIGID ASSEMBLY OF TWO CORE HALVES BELONGING TODIFFERENT MAGNETIC CIRCUIT, SAID ASSEMBLY HAVING EXPOSED NONCOLINEARPOLESHOE FACES, GRINDING SAID POLESHOE FACES UNTIL THEY ARESUBSTANTIALLY PLANO-PARALLEL, PLACING THE POLESHOE FACES OFCORRESPONDING CORE HALVES AGAINST THE TWO GROUND POLESHOE FACES OF THEASSEMBLY, AND MECHANICALLY SECURING SAID CORRESPONDING CORE HALVES INPOSITION.